With the rapid development of the information technology and multi-service wireless network, the demand for broadband wireless service increases constantly while spectrum which is non-renewable resource is scarce. According to the existing fixed spectrum allocation strategy, many spectrums that have been allocated to licensed users are idle in certain time periods, which results in low utility efficiency of spectrums and large waste of spectrums. With cognitive radio (CR) technology, the utility efficiency of spectrums may be improved, and insufficiency of spectrum resources may be mitigated. Therefore the cognitive radio (CR) technology becomes research hotspot in the field of wireless communications.
A device (which is referred to as “secondary device” herein) employing the cognitive radio technology opportunistically accesses an idle frequency hand of a licensed user equipment (which is referred to as “primary device” herein) without affecting the normal communication of the licensed user equipment, thereby realizing dynamic spectrum access and improving utility efficiency of spectrums.
Although insufficiency of spectrum resources can be mitigated with the cognitive radio technology, a large number of secondary devices accessing the idle frequency band of the primary device may result in significant interferences among users and frequent changes in network status. In a conventional cognitive multiple-input multiple-output (MIMO) system, information exchange usually requires joint information exchange between a base station and a user equipment in the cognitive system. The efficiency of information exchange is greatly decreased as the number of the user equipments increases.
In addition, it is also necessary to consider a case where the secondary devices have different priorities (or Quality of Service (QoS) levels).